Integrated circuits are often manufactured on a semiconductor substrate, such as a silicon wafer. The silicon wafer is typically a thin circular plate of silicon that is 150 or 200 or 300 millimeters in diameter and approximately 2 millimeters thick. Typically, a single wafer will have numerous devices which are integrated circuits formed in a lattice pattern. Each device consists of numerous layers of circuitry and collection of external bonding (and optional testing) pads. The bonding pads are small sites, typically 3 mils square, made usually with aluminum or other metals that eventually serve as the device's connections to the pin leads.
Probing involves contacting the bonding pads with probe tips to make an electrical (resistive) connection between the probe tips and the bonding pads or other pads. Accurate positioning of the pads under, or otherwise relative to, the tips is necessary both to avoid causing damage to the pads and to maintain the desired contact pressure that ensures good electrical contact.
Probe tips move or deform during the operation of probing. This action makes the probe tips scrub or slide across bond pads, balls, contact bumps, or contact surfaces of the wafer being tested. This mechanical action is necessary to break through the contamination and oxide on the probe tips and or the pads. Due to the mechanical action described, undesirable forces can be generated within a system.